Ignition system for a gas engine

ABSTRACT

An ignition device (22) is positioned in an ignition chamber (21) which in turn is positioned in a prechamber (11) in the cylinder head of an internal combustion engine. A valve controlling flow to and from the ignition chamber is opened to initiate ignition near top dead center of the compression stroke and is closed before the exhaust stroke to trap hot combustion gases in the ignition chamber. Very exacting control of ignition is achieved.

TECHNICAL FIELD

This invention relates to an internal combustion engine and a method foroperating such an internal combustion engine wherein the internalcombustion engine has a crankcase in which there is rotatably supporteda crankcase in which there is rotatably supported a crankshaft, to whichthere is articulated at least one connecting rod, which bears a pistonthat is movable in a cylinder head covered by a cylinder so as to form aworking space. An air-gas mixture is supplied to the working space byway of breathing ducts in the cylinder head. A prechamber is recessedinto the cylinder head and an ignition chamber is provided in theprechamber. The ignition chamber is opened and closed by a valve.

BACKGROUND OF THE INVENTION

The internal combustion engine shown in U.S. Pat. No. 5,067,458 has amain combustion chamber and an auxiliary combustion chamberinter-connected by a connecting duct. An ignition device is insertedinto the auxiliary combustion chamber. The connecting duct can beblocked in order to decouple the ignition device from the maincombustion chamber. By this prior art construction, the purging processbetween the auxiliary combustion chamber and the main combustion chamberis coupled to the ignition time and the auxiliary combustion chambermust be connected to the main combustion chamber over a long workingperiod.

Another ignition system for an internal combustion engine is known fromGerman patent document DE-OS 28 26 807. In this internal combustionengine, in successive working strokes, first an oxygen-containingmixture is compressed and thereby heated as well as thereafter ignited,whereupon the combustion gases expand. This working method is developedbecause at least part of the fuel employed is heated to at least itsignition temperature before introduction into the process, then injectedin the gaseous state into the oxygen-containing mixture in accordancewith a law governing the combustion process. This method and acorrespondingly designed internal combustion engine require a largeconstructional effort and are thus expensive in implementation, theignition control, or respectively, ignition of the mixture still beingsubject to fluctuations.

Another system is known from British patent GB-A 2, 031 513, whichdiscloses a two-substance system, wherein, pilot fuel is supplied to theinternal combustion engine via an injector nozzle, which pilot fuel isignited by a spark plug. This ignited pilot fuel then ignites the mainfuel located in another chamber.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to furnish an internal combustionengine and a method for operating the internal combustion engine thatpermits a very exact and reliable determination of the ignition time ofthe working substance.

According to the invention, this object is achieved by providing anignition chamber (including ignition device) which is inserted into theprechamber. The ignition chamber can be selectively closed off from theworking space at certain times and connected to the working space atother times in order to ignite working substance newly supplied to theworking space. The internal combustion engine designed for this methodis distinguished in that an ignition chamber is inserted into theprechamber and the ignition chamber can be tightly sealed off from theworking space via the prechamber, and in that the ignition chambercontains the ignition device. Reliable initiation and stable combustionof the working substance, which in the supplied state consists of afuel-air mixture, is guaranteed by this method and this design. Thefuel-air mixture is preferably a gas-air mixture, and the presentinvention is especially useful in stationary gas engines. The knownspark ignition for Otto-cycle engines has the disadvantage thatflame-core formation and the resulting combustion is subject to strongcyclical fluctuations. In the likewise known method of glow-plugignition, a combustible gas-air mixture in the combustion chamber isinitiated by a glow plug with a high surface temperature, stableinitiation being possible but the initiation time fluctuating. Glow-plugignition can be embodied both with and without temperature control forthe incandescent element. The embodiment with temperature control hasshorter, but still relatively unreproducible, initiation times. Thesedisadvantages and problems are avoided by the present invention. It hasbeen shown that the newly supplied working substance can be reliably anddependably ignited or initiated by means of the ignition device that canbe closed off in the ignition chamber. It is crucial that, at the timeof desired ignition (the ignition time), the ignition chamber isconnected to the working space, so that steady-state conditions prevailat the ignition device essentially up to the time of ignition. Very goodreproducibility of the initiation time is achieved, because, as a resultof the relatively large contact area between the mixture to be ignitedand the incandescent surface of the incandescent body, a flame core isformed that is several times larger than a flame core initiated by aspark ignition. This much larger flame core liberates far more energybecause of the chemical combustion reaction taking place therein than istransported out of the flame core to the environment by heat losses. Theflame core is therefore inherently stable. By this construction it is asif the cyclical fluctuations that are typical of the spark-ignitionOtto-cycle engine were eliminated. Further, the energy to be supplied tothe ignition device can be reduced in comparison with a known ignitiondevice, by which construction the service life of the ignition device isprolonged. With regard to the term initiation time used previously, itshould be stated that as generally defined this is the time intervalbetween the ignition time and the time at which 1% of the mixture hasreacted. In conventional spark ignitions, the ignition time can beestablished in an exactly definable way with high reproducibility, whichpermits reliable ignition control. The initiation time in conventionalspark ignitions, however, has poor reproducibility (fluctuations in the1% reaction time). By using the ignition device according to theinvention, it is possible to realize a highly reproducible initiationtime while maintaining a highly reproducible ignition time.

In development of the invention, a valve closing the ignition chamberoff from the working space is opened in order to begin ignition.Depending on the design of the internal combustion engine, the ignitionchamber is located immediately adjacent to the working space or in aprechamber that adjoins the working space.

In development of the invention, the valve is closed after ignition hastaken place. For this purpose a time is chosen that is optimized withrespect to complete initiation of the working substance in terms ofconsumption and exhaust emission in accordance with the applicablerequirements. Because the same pressure prevails both in the workingspace and in the prechamber, no large valve-closing or, respectively,valve-opening forces arise.

In development of the invention, the ignition chamber is thermallyinsulated on the inner wall. By this construction it is achieved that,on the one hand, the radiation losses of the ignition device between twosuccessive working cycles are very slight and, on the other hand, thereis no additional thermal burden on the adjacent components, particularlyon the cylinder head.

In development of the invention, the ignition chamber can be closed offfrom the prechamber or, respectively, the working space by use of avalve, and the valve is controlled by a hydraulically and/orelectrically operable control element. The selection of hydraulic and/orelectrical operation is made according to the circumstances of theinternal combustion engine in question, a role being played inparticular by the size of the valve and the hydraulic systemavailability.

In development of the invention, the hydraulic system is a high-pressuresystem, a solenoid-actuated valve being included in the setting and/orresetting line to the control element. The solenoid-actuated valveincludes a pilot valve that controls a high-pressure line in suchfashion that the high-pressure line can be connected to a low pressureline. The solenoid-actuated valve is, if appropriate, a known and testedvalve from injection technology, which is used to control injection inthe high-pressure fuel system in injection technology. The pilot valveis actuated by a solenoid, is arranged in an appropriate valve bodytransversely to the setting and/or resetting line, and in the closedstate permits unhindered flow in the high-pressure line via an annularspace in the valve body. In the open state of the pilot valve, thishigh-pressure line is then connected, via a restriction to the pilotvalve, to a low-pressure line arranged laterally next to thehigh-pressure line. Thus a certain minimum pressure remains present inthe overall system even in the open state.

It should be noted that in the control according to the invention, adigital temperature control--implemented by use of a digital signalprocessor--is used for the incandescent body. Very exact control is madepossible by this construction.

BRIEF DESCRIPTION OF THE DRAWING

Further advantageous developments of the invention can be inferred fromthe drawing, which illustrates an exemplary embodiment described in moredetail in the description that follows.

DETAILED DESCRIPTION OF THE INVENTION

The illustrated internal combustion engine includes a crankcase 1 inwhich a crankshaft 2 is rotatably supported.

Attached to the crankshaft 2 is a connecting rod 3, which bears a piston4, which is movable in a cylinder liner 5. The cylinder liner 5 or,respectively, the crankcase 1 is closed from above by a cylinder head 6,a working space 7 being formed between the piston 4 and the cylinderhead 6.

The intake and exhaust of the working substance in the form of gas andair takes place via an ordinary breathing apparatus having camshaft 8,partially shown valve drive 9, and partially shown breathing ducts 10.

Recessed in the cylinder head 6 is a prechamber 11, into which anignition chamber 21 is inserted. An ignition device 22 in the form of aspark plug or glow plug is inserted into the ignition chamber 21, whichignition device is operated in a controlled fashion during the operationof the internal combustion engine. The ignition chamber 21 can furtherbe closed off from the prechamber 11 by a valve 12. The valve 12 isactuated by a control element 13, which in turn is controlled by asolenoid-actuated valve 14. The solenoid-actuated valve 14 is driven byan electronic control mechanism 15. The control mechanism 15 can alsocontrol all other engine functions, in particular also the ignitiondevice. The solenoid-actuated valve 14 controls a high-pressure line16a, 16b, via which hydraulic fluid, in particular oil, is conveyed froma reservoir 17 to the control element 13. The reservoir 17 is filledwith hydraulic fluid from a tank 20 by a pump 18, which is driven by,for example, an electric motor 19. The solenoid-actuated valve 14 inthis design embodiment has a dual control function. In the controlprocess initiating ignition, the connection between the reservoir 17 andthe pressure cylinder located in the control element 13 is cleared andthe connection between the pressure cylinder and the tank return isblocked. In this control state, a piston located in the pressurecylinder will open the connection between the ignition chamber 21 andthe working space 7 (control state I). In the control process that endsignition, the connection between the reservoir 17 and the pressurecylinder located in the control element 13 is blocked and the connectionbetween the pressure cylinder and the tank return is cleared. The pistonis pushed back by a return spring and thus closes the connection betweenignition chamber 21 and working space 7.

OPERATION

The mode of operation of the internal combustion engine according to theinvention is a follows. First, the internal combustion engine is a gasengine operating by the four-cycle process and having a plurality ofcylinder units. Supplied working substance in the form of an air-gasmixture is compressed in the working space 7 by the piston 4 and must beignited in the region of the firing top dead center position of thereciprocating piston. This takes place by operation of the ignitiondevice 22 arranged in the ignition chamber 21. In the time intervalshortly before the desired ignition of the fresh mixture located in theworking space 7 (and also the prechamber 11), the valve 12 is opened bythe piston of the pressure cylinder in the control element 13 upon thelatter being energized by the control mechanism 15, so that the freshmixture enters the ignition chamber 21 and is ignited by the ignitiondevice. After ignition has taken place, the valve 12 is closed again(the control mechanism 15 de-energizes the control element 13 and thereturn spring closes the valve 12) and thus the ignition device isseparated from the working space until the next working cycle.

What is claimed is:
 1. In an internal combustion engine having acrankcase in which there is a rotatably supported crankshaft, to whichthere is articulated at least one connecting rod, which bears a pistonthat is movable in a cylinder covered by a cylinder head so as to form aworking space, said cylinder head including ducts from supplying anair/gas mixture to the working space, the combination comprising:aprechamber (11) recessed into said cylinder head and in free flowcommunication with said working space (7), an ignition chamber (21)extending downwardly from said cylinder head and into said prechamber(11) whereby the major portion of the exterior of said ignition chamberis exposed to the combustion gases in said prechamber, a flow controldevice including a valve (12) in said ignition chamber (21) having anopen position in which said ignition chamber is in free flowcommunication with said working space (7) and a closed position in whichsaid ignition chamber (21) is closed, a control mechanism for cyclicallyopening and closing said valve (12), said control mechanism opening saidvalve (12) near the top dead center position of said piston at the endof the compression stroke of said piston and subsequently closing saidvalve (12) during combustion of said compressed air/gas mixture prior tocompletion of the power stroke of said piston, and an ignition device(22) in said ignition chamber (21) operable to ignite said compressedair/gas mixture upon opening of said valve (12).
 2. The internalcombustion engine of claim 1 wherein said ignition chamber (21) includesan interior wall and wherein said interior wall is thermally insulated.3. The internal combustion engine of claim 1 wherein said controlmechanism for operating said valve (12) includes a control element (13)in actuating relation to said valve (12).
 4. The internal combustionengine of claim 3 wherein said flow control device includes a highpressure hydraulic control and wherein said control mechanism includes asolenoid-actuated valve (14) operable to actuate said control element(13).